196 ESSAYS BIOGRAPHICAL AND CHEMICAL 



moving about in a watery solution, they are named ' ions,' 

 a Greek word, which means ' wanderers.' 



But an ion is not merely a wandering particle; the 

 moving particles of sugar are not called ions. The ions 

 contained in a solution of salt have another peculiarity ; 

 one has gained, and the other has lost, what we may term 

 an atom of electricity. Now what is electricity ? 



It used to be believed, formerly, that there were two 

 kinds of electricity, one called positive and the other 

 negative. At that time it would not have been possible 

 to answer the question. But recent researches make it 

 probable that what used to be called negative electricity 

 is really a substance. Indeed the relative weight of its 

 particles has been measured; each is about one seven- 

 hundredth of the mass of an atom of hydrogen : and the 

 mass of an atom of hydrogen is the smallest of all 

 masses of what we have been used to call matter. 



Atoms of electricity are named ' electrons ' ; they appear 

 to be all of one kind. The metal sodium, and indeed all 

 other metals, may be regarded as compound of electrons 

 with a stuff which may be named ' sodion ' for sodium, 

 ' cuprion ' for copper, ' ferrion ' for iron, and so on. When 

 sodium loses an electron it becomes ' sodion ' ; when iron 

 loses three electrons it becomes ' ferrion,' and similarly 

 with the rest. 



How can sodium be made to lose its electron ? This 

 happens when it enters into combination. When sodium 

 is heated in air, which contains oxygen gas, it burns, and 

 is said to unite or combine with oxygen ; burning appears 

 to be accompanied by a transference of an electron from 

 the sodium to the oxygen. Common salt may be made 

 by heating sodium in chlorine gas ; it takes fire, burns 

 and is changed into white ordinary salt. It has lost an 

 electron ; chlorine has gained one. 



When dissolved in water, the sodium exists in the water 



